I have never been a crop sprayer but am ex RAF where I was taught to fly low to survive. It was always drilled into us that the kill probabability of flying into the ground (100%!) was always higher than being shot down by a SAM or Air-to-Air missile......
The tips already given though hold good, "up" trim, lookout and knowing the performance limits of the ac and in intimate knowledge of the cockpit are essential. Practice on clouds first and then work down gradually.....
If possible, get some dual time with an experienced pilot first and, get the right PPE, a good harness, helmet, flying suit and gloves. Finally, make sure there are no loose articles in the cockpit - you don't need a control restriction or a distraction.
Just my two cents worth but remember, I never said I have had first hand experience of ever spraying crops, apart from when having a slash on exercise!
MB